1. Field Of The Invention
The invention relates to a method for driving a picture tube, the front pane of the picture tube having a vertical as well as a horizontal glass thickness which varies in accordance with a known function and where a voltage difference, consisting of a DC voltage level determining the background brightness and the video signal voltage, is applied to the two electrodes which determine the beam current of the cathode beam, as well as to a circuit assembly for executing the method.
2. The Prior Art
Because of the requirement for having a display surface on video screens which is curved as little as possible, picture tubes are in use today having, because of the large radius of curvature of the front pane, a glass thickness which continuously increases in the direction of the edge of the front pane in order to maintain structural stability. Furthermore, to improve contrast, the front pane in such video screens is customarily colored in such a way that transparency lies at approximately 50%. Since, for technical reasons, the glass can only be evenly colored, the transparency is reversely proportional to the glass thickness. For this reason, when such picture tubes are used, there is an uneven brightness distribution on the video screen. Maximum brightness occurs at the center of the screen and is evenly reduced in the direction for the corners of the video screen.
The conditions described above have the result that, in particular in connection with video screen displays of data processing devices, the eyes of the operator are severely stressed exactly because of this uneven brightness distribution.